Xilinx RocketIO User Manual page 86

R
FIBRE_CHAN does not need to define the attributes CRC_START_OF_PKT and
CRC_END_OF_PKT. Both USER_MODE and FIBRE_CHAN, however, disregard SOP and EOP
in CRC computation.
Designs should generate only the EOP frame delimiter for a beginning running disparity (RD) that
is negative. (These are the frame delimiters that begin with /K28.5/D21.4/ or /K28.5/D10.4/.) Never
generate the EOP frame delimiter for a beginning RD that is positive. (These are the frame
delimiters that begin with /K28.5/D21.5/ or /K28.5/D10.5/.) When the RocketIO CRC determines
that the running disparity must be inverted to satisfy Fibre Channel requirements, it will convert the
second byte of the EOP frame delimiter (D21.4 or D10.4) to the value required to invert the running
disparity (D21.5 or D10.5).
Note that CRC generation for EOP requires that the transmitted K28.5 be left-justified in the MGT's
internal two-byte data path. Observing the following restrictions assures correct alignment of the
packet delimiters:
•
•
•
ETHERNET
The Ethernet CRC is more complex
the CRC. The extension bytes are special "K" characters in special cases. The extension bytes are
untouched by the CRC as are the Trail bits, which are added to maintain packet length.
SOP Preamble
n Bytes
Designs should generate only the /K28.5/D16.2/ IDLE sequence for transmission, never
/K28.5/D5.6/. When the RocketIO CRC determines that the running disparity must be inverted to
satisfy Gigabit Ethernet requirements, it will convert the first /K28.5/D16.2/ IDLE following a
packet to /K28.5/D5.6/, performing the necessary conversion.
86
SOP
RXCHECKINGCRC
RXCRCERR
Figure 2-24: USER_MODE / FIBRE_CHAN Mode
4-byte data path: K28.5 must appear in TXDATA[31:24] or TXDATA[15:8].
2-byte data path: K28.5 must appear in TXDATA[15:8].
1-byte data path: K28.5 must be strobed into the MGT on rising TXUSRCLK2 only when
TXUSRCLK is High.
Note:
Minimum data length for this mode is 24 bytes, not including the CRC placeholder.
Note:
For correct operation of the Gigabit Ethernet CRC function, the frames that are
transmitted and received must comply with the IEEE 802.3 specifications regarding Gigabit
Ethernet, including the preamble maximum length.
SOF DATA
Figure 2-25: Ethernet Mode
Chapter 2: Digital Design Considerations
DATA R R
0 1
(Figure 2-25). The SOP, EOP, and Preamble are neglected by
Pad Bits R 0 R 1
2 to 3 Bytes
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R R EOP
2 3
R 2 R 3 EOP Trail Bits
UG024_13_101602
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
UG024_12_022803